Atomic layer etch of tungsten for enhanced tungsten deposition fill

ABSTRACT

Methods of depositing tungsten into high aspect ratio features using a dep-etch-dep process integrating various deposition techniques with alternating pulses of surface modification and removal during etch are provided herein.

INCORPORATION BY REFERENCE

An Application Data Sheet is filed concurrently with this specificationas part of the present application. Each application that the presentapplication claims benefit of or priority to as identified in theconcurrently filed Application Data Sheet is incorporated by referenceherein in their entireties and for all purposes.

BACKGROUND

Semiconductor fabrication processes often involve deposition of metals,such as tungsten, into features, such as vias or trenches, to formcontacts or interconnects. However, as devices shrink, features becomesmaller and harder to fill, particularly in advanced logic and memoryapplications.

SUMMARY

Provided herein are methods of filling features on substrates. Oneaspect involves a method of filling features on a substrate by (a)depositing a first amount of a metal in a feature; and (b) directionallyetching the metal at or near an opening of the feature relative to aninterior region of the feature by (i) modifying the surface of thedeposited metal by exposing the metal to a halogen-containing gas; and(ii) exposing the modified surface to an activation gas to selectivelyetch the metal. The method may further include repeating (a) and (b).

In various embodiments, the metal contains one of titanium, tantalum,nickel, cobalt, or molybdenum. In some embodiments, the metal containstungsten.

In some embodiments, the halogen-containing gas is selected from thegroup consisting of chlorine, bromine, iodine, sulfur hexafluoride,silicon tetrafluoride, boron trichloride, or combinations thereof. Insome embodiments, the activation gas is an inert gas, such as neon,krypton, argon, or combinations thereof.

The method may further include applying a bias during at least one of(i) and (ii). The bias power may be less than a threshold bias power.The bias power may be less than about 80 Vb.

In various embodiments, (b) includes a self-limiting reaction. In someembodiments, the substrate includes features having different sizeopenings. The feature may have an aspect ratio of at least 3:1. In someembodiments, the opening is less than 20 nm wide.

In some embodiments, (a) and (b) are performed without breaking vacuum.In some embodiments, (a) and (b) are performed in the same chamber. Insome embodiments, (a) and (b) are performed in different chambers of thesame tool.

The method may further include igniting a plasma during at least one of(i) and (ii). The plasma power may be between about 0 W and about 1000W.

Another aspect may involve a method including (a) partially filling afeature with tungsten; (b) directionally etching tungsten at or near theopening of the feature by exposing the substrate to alternating pulsesof a halogen-containing gas and an activation gas; and (c) filling thefeature with tungsten.

In some embodiments, a bias is applied during (b). In some embodiments,the bias is applied during (b) at a threshold bias power.

In various embodiments, (a) and (b) are performed without breakingvacuum. In some embodiments, (a) and (b) are performed in the samechamber. The method may further include repeating (a) and (b). Fillingthe feature may include repeating (a) and (b).

The tungsten may be deposited by CVD. In some embodiments, the tungstenis deposited by ALD. The tungsten may be deposited by exposing thesubstrate to alternating pulses of a tungsten-containing precursor and areducing agent. The tungsten may be deposited using achlorine-containing tungsten precursor. In some embodiments, thetungsten is fluorine-free tungsten.

Another aspect involves an apparatus for processing semiconductorsubstrates, the apparatus including: a process chamber including ashowerhead and a substrate support, a plasma generator, and a controllerhaving at least one processor and a memory, whereby the at least oneprocessor and the memory are communicatively connected with one another,the at least one processor is at least operatively connected with theflow-control hardware, and the memory stores machine-readableinstructions for: introducing a tungsten-containing precursor and areducing agent to the chamber to deposit tungsten on a substrate;introducing a halogen-containing gas to modify the surface of thetungsten; and introducing an activation gas and igniting a plasma toetch at least part of the modified surface of tungsten.

The substrate support may include a bias, and the memory may furtherstore machine-readable instructions for setting the bias power less thanabout 80 Vb during (iii). In some embodiments, the memory further storesmachine-readable instructions for igniting a plasma during (ii).

In some embodiments, the memory further stores machine-readableinstructions for repeating (ii) and (iii) in cycles. In someembodiments, the memory further stores machine-readable instructions forafter performing (ii) and (iii), repeating (i).

These and other aspects are described further below with reference tothe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an example of atomic layer etchingof film on a substrate.

FIG. 2 is a schematic illustration of a feature undergoing operations ofcertain disclosed embodiments.

FIG. 3 is a process flow diagram depicting operations performed inaccordance with certain disclosed embodiments.

FIG. 4 is a graph of calculated normal incident sputter yield oftungsten using argon ions.

FIG. 5 is a timing schematic diagram depicting an example of operationsperformed in accordance with certain disclosed embodiments.

FIG. 6 is a schematic diagram of an example process chamber forperforming certain disclosed embodiments.

FIG. 7 is a schematic diagram of an example process apparatus forperforming certain disclosed embodiments.

FIG. 8 is a graph of experimental data collected for etch rates oftungsten over chlorination bias power.

FIG. 9A is an image of a feature with tungsten.

FIG. 9B is an image of a feature with tungsten deposited in accordancewith certain disclosed embodiments.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a thorough understanding of the presented embodiments. Thedisclosed embodiments may be practiced without some or all of thesespecific details. In other instances, well-known process operations havenot been described in detail to not unnecessarily obscure the disclosedembodiments. While the disclosed embodiments will be described inconjunction with the specific embodiments, it will be understood that itis not intended to limit the disclosed embodiments.

Semiconductor fabrication processes often involve deposition of metalsinto features, such as vias or trenches, to form contacts orinterconnects. Tungsten is often deposited into such features usingchemical vapor deposition (CVD), whereby a substrate including featuresto be filled is exposed to a tungsten-containing precursor and areducing agent to deposit the tungsten into the features. However, asdevices shrink, features become smaller and harder to fill by CVD,particularly in advanced logic and memory applications. For example,features may have a high aspect ratio, such as at least about 3:1. Somefeatures may have a small opening of less than about 20 nm. Somefeatures may also include a re-entrant feature profile, which is furtherdescribed below with respect to FIG. 2. For features in advancedtechnology nodes, the deposition rate at or near the opening of thefeature may be faster than deposition at the bottom of the feature,which causes the opening to close before the entire feature is filled,leaving behind a void or gap in the feature. The presence of such gapsmay be detrimental to the performance and reliability of thesemiconductor device, and ultimately the semiconductor product.

Additionally, some substrates may include features of various sizes. Asa result, features are filled or the openings of the features are closedmore quickly in smaller features than in larger features, and largerfeatures may not be completely filled. The small opening and high aspectratio of features may also cause non-conformal deposition of tungstenwithin a feature. Additionally, in re-entrant feature profiles caused byconventional deposition techniques and possible overhang of anunderlying barrier or glue layer due to non-conformal coverage on thefeature, the feature may have a net re-entrant sidewall profile, whichmakes complete fill of the feature challenging.

One method of depositing tungsten into features having small openingsincludes exposing a partially filled feature to a reactive species suchas a fluorine-containing species generated in a remote plasma generatorand operating in a mass transfer limited process regime to removepreviously deposited tungsten at the opening of the feature and therebyopen the feature to allow further deposition of tungsten into thefeature, thereby facilitating complete void-free fill. However, whilesuch methods may be effective in depositing void-free tungsten intosmall features, the amount of deposition and etch processes used to filla larger feature may vary. Additionally, fluorine-containing reactivespecies are very reactive and therefore etch tungsten quickly, such thatetch conditions are modulated to prevent from etching too much tungsten.If the entirety of the deposited tungsten is removed, it becomesdifficult to subsequently re-nucleate the exposed surface with tungstento fill the feature. For example, prior to depositing any tungsten, afeature is often lined with a barrier layer, such as a titanium nitridebarrier layer, and the feature may be exposed to precursors to deposit atungsten nucleation layer by methods such as atomic layer deposition(ALD). However, if a fluorine-containing reactive species removes theentire nucleation layer due to its high reactivity and etch rate, thetitanium nitride barrier layer is exposed and tungsten is nucleated onthe surface a second time, thereby reducing throughput. In someembodiments, the fluorine-containing reactive species may etch at leastsome of or the entire barrier layer, which may cause a second tungstendeposition to be incomplete as some of the tungsten nucleation layer maybe missing on the substrate.

Provided herein are methods of filling features with tungsten using anintegrated deposition and atomic layer etching (ALE) process. ALE is atechnique that removes thin layers of material using sequentialself-limiting reactions. Generally, ALE may be performed using anysuitable technique. Examples of atomic layer etching techniques aredescribed in U.S. Pat. No. 8,883,028, issued on Nov. 11, 2014; and U.S.Pat. No. 8,808,561, issued on Aug. 19, 2014, which are hereinincorporated by reference for purposes of describing example atomiclayer etching techniques. In various embodiments, ALE may be performedwith plasma, or may be performed thermally. The concept of an “ALEcycle” is relevant to the discussion of various embodiments herein.Generally an ALE cycle is the minimum set of operations used to performan etch process one time, such as etching a monolayer. The result of onecycle is that at least some of a film layer on a substrate surface isetched. Typically, an ALE cycle includes a modification operation toform a reactive layer, followed by a removal operation to remove or etchonly this modified layer. The cycle may include certain ancillaryoperations such as sweeping one of the reactants or byproducts.Generally, a cycle contains one instance of a unique sequence ofoperations. As an example, an ALE cycle may include the followingoperations: (i) delivery of a reactant gas, which may be in a plasma,(ii) purging of the reactant gas from the chamber, (iii) delivery of aremoval gas and an optional plasma, and (iv) purging of the chamber. Insome embodiments, etching may be performed nonconformally on asubstrate, such as a substrate with topography and/or features.

FIG. 1 shows two example schematic illustrations of an ALE cycle.Diagrams 171 a-171 e show a generic ALE cycle. In 171 a, a substrate isprovided. In 171 b, the surface of the substrate is modified. In 171 c,the chemical used to modify the substrate is purged. In 171 d, themodified layer is being etched. In 171 e, the modified layer is removed.Similarly, diagrams 172 a-172 e show an example of an ALE cycle foretching a tungsten film. In 172 a, a tungsten substrate is provided,which includes many tungsten atoms. In 172 b, reactant gas chlorine isintroduced to the substrate, which modifies the surface of thesubstrate. In some embodiments, a chlorine reactant may also bedelivered as atomic chlorine in a plasma which may not cause directetching of a tungsten substrate. The schematic in 172 b shows that somechlorine is adsorbed onto the surface of the substrate as an example.Although chlorine (Cl₂) is depicted in FIG. 1, any chlorine-containingcompound or other suitable reactant may be used. In 172 c, the reactantgas chlorine is purged from the chamber. In 172 d, a removal gas argonis introduced with a directional plasma, as indicated by the Ar⁺ plasmaspecies and arrows, to remove the modified surface of the substrate. Theactivated etching involves the use of inert ions (e.g., Ar⁺) operatingwith energy below the sputtering threshold to energize the adsorbspecies (e.g., Cl species) to etch away the substrate one monolayer at atime. During this operation, a bias is applied to the substrate toattract ions toward it. In 172 e, the chamber is purged and thebyproducts are removed.

The etch rate for ALE processes is lower than that of a fluorine-basedremote plasma etch, but ALE etches more uniformly due to theself-limiting nature of the surface reactions. Thus, ALE processesprovide more control over the etching operations, particularly in largerfeatures, such that the amount of material removed in each cycle islimited and not etched too quickly so as to prevent completely etchingof material from the surface of the feature. Deposition processesdescribed herein may be controlled by toggling pressure of the chamberand temperature of the substrate, both of which affect adsorption of amodification chemistry during ALE. Processes may also be controlled bymodulating a substrate bias during one or more operations performed inALE and modulating modification chemistry flow and chemistry. Depositionprocesses may also depend on the chemistry of the metal to be depositedinto features.

Disclosed embodiments may involve deposition of a metal, such astungsten, in a feature by any suitable method, including ALD, CVD,plasma enhanced ALD (PEALD), plasma enhanced CVD (PECVD), or physicalvapor deposition (PVD); adsorption of a halogen-containing gas andoptional exposure to a plasma to modify a surface of the depositedmetal; exposure to an activation gas to remove the modified surface; andfurther deposition of the metal to fill the feature. FIG. 2 provides anexample schematic illustration of a feature undergoing variousoperations in accordance with disclosed embodiments. In 201, a substrate210 is shown with a feature 212, which includes a TiN barrier layer 214deposited conformally in the feature and tungsten 216 conformallydeposited by ALD over the TiN barrier layer 214. In 203, after thefeature 212 is exposed to a halogen-containing gas to modify the surfaceof the deposited tungsten 216, the feature 212 is exposed to anactivation gas, such as a gas including argon ions or neon, or krypton,which may etch the tungsten 216 at or near the opening 218 a of thefeature 212 directionally, such as by using a low bias. In 205, thefeature 212 has been opened, leaving a feature opening 218 b. In 207,the feature 212 is subsequently filled with tungsten by CVD to yield avoid-free tungsten filled feature.

FIG. 3 provides a process flow diagram depicting operations in a methodin accordance with disclosed embodiments. While the description belowfocuses on tungsten feature fill, aspects of the disclosure may also beimplemented in filling features with other materials. For example,feature fill using one or more techniques described herein may be usedto fill features with other materials including othertungsten-containing materials (e.g., tungsten nitride (WN) and tungstencarbide (WC)), titanium-containing materials (e.g., titanium (Ti),titanium nitride (TiN), titanium silicide (TiSi), titanium carbide(TiC), and titanium aluminide (TiAl)), tantalum-containing materials(e.g., tantalum (Ta), and tantalum nitride (TaN)), molybdenum-containingmaterials, cobalt-containing materials, and nickel-containing materials(e.g., nickel (Ni) and nickel silicide (NiSi)). In various embodiments,features may be filled with another metal instead of or in combinationwith tungsten. For example, cobalt or molybdenum may be used to fillfeatures.

In operation 301 of FIG. 3, a substrate is provided to a chamber. Thesubstrate may be a silicon wafer, e.g., a 200-mm wafer, a 300-mm wafer,or a 450-mm wafer, including wafers having one or more layers ofmaterial such as dielectric, conducting, or semi-conducting materialdeposited thereon. A patterned substrate may have “features” such asvias or contact holes, which may be characterized by one or more ofnarrow and/or re-entrant openings, constrictions within the features,and high aspect ratios. The features may be formed in one or more of theabove described layers. One example of a feature is a hole or via in asemiconductor substrate or a layer on the substrate. Another example isa trench in a substrate or layer. In various embodiments, the featuremay have an under-layer, such as a barrier layer or adhesion layer.Non-limiting examples of under-layers include dielectric layers andconducting layers, e.g., silicon oxides, silicon nitrides, siliconcarbides, metal oxides, metal nitrides, metal carbides, and metallayers.

Examples of applications include logic and memory contact fill, DRAMburied wordline fill, vertically integrated memory gate/wordline fill,and 3-D integration with through-silicon vias (TSVs). The methodsdescribed herein can be used to fill vertical features, such as intungsten vias, and horizontal features, such as vertical NAND (VNAND)wordlines.

In various embodiments, types of substrates fabricated from performingdisclosed embodiments may depend on the aspect ratios of features on thesubstrate prior to performing disclosed embodiments. In someembodiments, features on a substrate provided in operation 301 may havean aspect ratio of at least about 2:1, at least about 3:1, at leastabout 4:1, at least about 6:1, at least about 10:1, or higher. Thefeature may also have a dimension near the opening, e.g., an openingdiameter or line width of between about 5 nm to 500 nm, for examplebetween about 25 nm and about 300 nm. Disclosed methods may be performedon substrates with features having an opening less than about 20 nm. A“small” feature may be defined as a feature having an opening diameteror line width less than that of a “large” feature in relative terms.Large features may have an opening diameter or a critical dimension atleast 1.5 times, or at least 2 times, or at least 5 times, or at least10 times or more than 10 times larger than the critical dimension ofsmall features. Examples of “small” features include features having anopening diameter between about 1 nm and about 2 nm. Examples of “large”features include features having an opening diameter on the order ofhundreds of nanometers to about 1 micron.

A via, trench or other recessed feature may be referred to as anunfilled feature or a feature. According to various embodiments, thefeature profile may narrow gradually and/or include an overhang at thefeature opening. A re-entrant profile is one that narrows from thebottom, closed end, or interior of the feature to the feature opening. Are-entrant profile may be generated by asymmetric etching kineticsduring patterning and/or the overhang due to non-conformal film stepcoverage in the previous film deposition, such as deposition of adiffusion barrier. In various examples, the feature may have a widthsmaller in the opening at the top of the feature than the width of themiddle and/or bottom of the feature.

In operation 303, tungsten is deposited over the substrate such as byexposing the substrate to a tungsten-containing precursor and a reducingagent to partially fill a feature on the substrate. Exampletungsten-containing precursors include tungsten-containing halideprecursors, which may include tungsten fluorides such as WF₆; andtungsten chlorides such as WCl₆, W(CO)₆, and WC's. In some embodiments,metal-organic tungsten-containing precursors may be used. Examplereducing agents include hydrogen, boranes (such as B₂H₆), silanes (suchas SiH₄), and germanes (such as GeH₄).

In some embodiments, tungsten is deposited conformally. In someimplementations, operation 303 involves deposition of a tungstennucleation layer, followed by bulk deposition.

Any suitable method for depositing tungsten may be used, such as ALD,CVD, PECVD, PEALD, or PVD. For the example provided herein, tungsten maybe deposited conformally into a feature by ALD. For example, in someembodiments, a tungsten nucleation layer is deposited by sequentiallypulsing a tungsten-containing precursor and one or more reducing agentsto form a tungsten nucleation layer by an ALD or pulsed nucleation layer(PNL) process. In some implementations, operation 303 may involve onlybulk deposition and no nucleation layer deposition, if, for example, thefeature includes an under-layer that supports tungsten deposition. Bulkdeposition may be deposited by chemical vapor deposition and isdescribed further below.

In features that include constrictions or are otherwise susceptible topinch-off, operation 303 can be performed at least until the feature ispinched off. Features having different sizes may pinch off at differenttimes. In conformal deposition, deposition starts from each surface andprogresses with growth generally orthogonal to the surface. Tungstengrowth in features starts from each sidewall and progresses until thegrowth pinches off the feature. In some implementations, the amount oftungsten deposited operation 303 can be determined based on thenarrowest feature dimension.

In various embodiments, operation 303 may be performed such that theopening of the feature is closed. In some embodiments, a seam may beformed at or near the opening of the feature. For the purposes of thisdescription, “near the opening” is defined as an approximate position oran area within the feature (i.e., along the side wall of the feature)corresponding to between about 0-10% of the feature depth measured fromthe field region. In certain embodiments, the area near the openingcorresponds to the area at the opening. Further, “inside the feature” orthe “interior of the feature” is defined as an approximate position oran area within the feature corresponding to between about 20%-60% of thefeature depth measured from the field region on the top of the feature.Typically, when values for certain parameters (e.g., thicknesses) arespecified “near the opening” or “inside the feature”, these valuesrepresent a measurement or an average of multiple measurements takenwithin these positions/areas.

In operation 305, the substrate is directionally or preferentiallyetched by atomic layer etching. “Directional” or “preferential” as usedherein may be defined as etching more material at or near the top of thefeature than in the rest of the feature, such as inside or interior ofthe feature. Atomic layer etching involves a surface modification and anactivation operation. In some embodiments, a carrier gas, which mayinclude N₂, Ar, Ne, He, and combinations thereof, is continuously flowedduring operation 305. In some embodiments, a carrier gas is only usedduring a removal process during operation 305. The carrier gas may beused as a purge gas in some operations as described below. In someembodiments, another reactant gas, such as oxygen, is used duringoperation 305 to remove a modified layer. In some embodiments, a carriergas is not flowed during removal.

In operation 315, the substrate is exposed to a modification chemistryto modify a surface of the substrate. The modification chemistry may bea gas or a plasma or reactive species. The modification operation formsa thin, reactive surface layer with a thickness that is more easilyremoved than un-modified material. The modification operation may beperformed such that spontaneous etching of the substrate is prevented.

In a modification operation, a substrate may be modified using ahalogen-containing chemistry. For example, a substrate may bechlorinated by introducing chlorine into the chamber. Chlorine is usedas an example modification chemistry in disclosed embodiments, but itwill be understood that in some embodiments, a different modificationchemistry is introduced into the chamber. Examples include bromine,iodine, sulfur hexafluoride, silicon tetrafluoride, and borontrichloride (BCl₃). Additional examples of etching metals by ALE arefurther described in U.S. Patent Application No. 62/207,250, filed onAug. 19, 2015, titled “ATOMIC LAYER ETCHING OF TUNGSTEN AND OTHERMETALS”, which is herein incorporated by reference in its entirety.

In various embodiments, a fluorine chemistry is not used to preventchemical etching that may not be etched in monolayers. For example,nitrogen trifluoride (NF₃) can be highly reactive in a plasma and mayspontaneously etch the substrate rather than etch the substrateconformally in layers. However, in some embodiments, a highly reactivehalogen-containing chemistry such as ClF₃ may be used to etch othermaterials, such as materials that are less susceptible to spontaneousetching.

The modification chemistry may be selected depending on the type andchemistry of the substrate to be etched. In some embodiments, chlorinemay react with the substrate or may be adsorbed onto the surface of thesubstrate. In various embodiments, chlorine is introduced into thechamber in a gaseous form and may be optionally accompanied by a carriergas which may be any of those described above.

In some embodiments, a chlorine-based plasma may be generated duringthis operation. The species generated from a chlorine-based plasma canbe generated in situ by forming a plasma in the process chamber housingthe substrate or they can be generated remotely in a process chamberthat does not house the substrate such as a remote plasma generator, andcan be supplied into the process chamber housing the substrate. Invarious embodiments, the plasma may be an inductively coupled plasma ora capacitively coupled plasma or a microwave plasma. Power for aninductively coupled plasma may be set at between about 50 W and about2000 W, such as about 900 W. Power may be set at a low enough level soas not to cause direct plasma etching of the substrate.

In some embodiments, a plasma is not used and chlorine may be introducedthermally into the chamber. The energy of dissociation of Cl₂ to Cl is2.51 eV. In some embodiments, this energy may be applied using thermalor other radiative energy sources during this operation. In someembodiments, chlorine may be heated at sufficiently high temperatures todecompose chlorine into chlorine atoms capable of adsorbing onto thesurface of a substrate.

In various embodiments, a bias is applied during operation 315. A lowbias power may be used to prevent spontaneous etching by themodification chemistry on the surface of the substrate while allowingthe modification chemistry adsorb on the surface of the deposited metaland enter a seam that may be formed at or near the opening of a feature.For example, a bias may be applied between about 0V and about 200V. Thebias may be used to establish a gradient of modification chemistrythroughout the feature depth. By appropriately controlling the bias aswell as other parameters such as pressure, the degree of modification(and of ALE) can be controlled throughout the feature depth. In oneexample, more chlorine may be adsorbed at or near the top of features,or at or near the openings of features, than in the bottom and on theside walls. The bias is applied in such a way so as not to causephysical sputtering of the substrate. In some embodiments, a bias maynot be used. In some embodiments, a bias may not be used if the openingsof features are large enough. An example pressure range during operation315 may be between about 30 mTorr and about 80 mTorr.

In some embodiments, a purge may be performed after a modificationoperation. In a purge operation, non-surface-bound active chlorinespecies may be removed from the process chamber. This can be done bypurging and/or evacuating the process chamber to remove non-adsorbedmodification chemistry, without removing the adsorbed layer. The speciesgenerated in a chlorine-based plasma can be removed by stopping theplasma and allowing the remaining species to decay, optionally combinedwith purging and/or evacuation of the chamber. Purging can be done usingany inert gas such as N₂, Ar, Ne, He, and their combinations.

In operation 335, the modified layer is removed from the substrate usingan activated removal gas, such as an activating gas, ion bombardmentgas, or chemically reactive gas. The activated removal gas may be aninert gas. For example, argon may be used. In some embodiments, neon orkrypton may be used. In a removal operation, the substrate may beexposed to an energy source (e.g. activating or ion bombardment gas orchemically reactive species that induces removal), such as argon orhelium, to etch the substrate by directional ion bombardment. In someembodiments, the removal operation may be performed by low energy ionbombardment. In some embodiments, removal may be isotropic.

The amount of removal gas may be controlled such as to etch only atargeted amount of material. In various embodiments, the pressure of thechamber may vary between the modification and removal operations. Thepressure of the removal gas may depend on the size of the chamber, theflow rate of the removal gas, the temperature of the reactor, the typeof substrate, the flow rate of any carrier gases, and the amount oftungsten to be etched. An example pressure range during operation 335may be between about 1 mTorr and about 15 mTorr.

During removal, a bias may be optionally applied to facilitatedirectional ion bombardment. The bias power is selected to preventsputtering but allow the removal gas to enter the feature and etch thetungsten at or near the opening of the feature to thereby open it. Thebias power may be selected depending on the threshold sputter yield ofthe activated removal gas with the deposited metal on the substrate.Sputtering as used herein may refer to physical removal of at least someof a surface of a substrate. Ion bombardment may refer to physicalbombardment of a species onto a surface of a substrate.

FIG. 4 shows an example sputter yield calculated based on “EnergyDependence of the Yields of Ion-Induced Sputtering of Monatomic Solids”by N. Matsunami, Y. Yamamura, Y. Itikawa, N. Itoh, Y. Kazumata, S.Miyagawa, K. Morita, R. Shimizu, and H. Tawara, IPPJ-AM-32 (Institute ofPlasma Physics, Nagoya University, Japan, 1983).

The figure shows the calculated normal incidence sputter yield oftungsten with argon atoms versus argon ion energy (or threshold biaspower). The calculation used a value of 32 eV for the sputter threshold.Slightly above the threshold, namely at 40 eV argon ion energy, thesputter yield seems to be about 0.001 atoms/ion. However, at 80 eV ionenergy, it has increased by a factor of 30. This example curve indicatesthe maximum argon ion energy sufficient to etch the metal whilepreventing sputtering of argon on the substrate. While FIG. 4 provides aqualitative representation of a sputter threshold curve, a sputterthreshold may be experimentally determined for a particular system andmaximum tolerable sputter yield. For one system, sputtering of tungstenis observed at 80 Vb for argon ions. As such, the bias power duringtungsten removal using argon ions may be set at less than about 80 Vb,or less than about 50 Vb, or between about 50 Vb and 80 Vb. In someembodiments, operation 335 may be performed above the threshold biaspower if some small amount of sputtering is tolerable. There may also bea removal threshold voltage, below which removal does not occur,depending on the particular process. It should be noted that the sputterthreshold varies according to the metal, metal compound, or othermaterial to be etched.

In some embodiments, the chamber may be purged after a removaloperation. Purge processes may be any of those used for a purge afteroperation 315.

Returning to FIG. 3, operations 315 and 335 may be optionally repeatedas necessary to fill the feature. In operation 307, it is determinedwhether the feature has been sufficiently filled. If not, operations 303and 305 may be repeated. In some embodiments, operation 303 is repeatedand the feature may be sufficiently filled such that operation 305 maynot be performed again. In some embodiments, operations 303 and 305 areperformed until features are sufficiently filled. In some embodiments,features may be sufficiently filled after performing operation 303 inone of the repeated operations, such that operation 305 is not performedafter features are filled. In some embodiments, operations 303 and 305are performed in the same chamber. In some embodiments, operations 303and 305 are performed in the same tool. In some embodiments, operations303 and 305 are performed without breaking vacuum. In some embodiments,repeated cycles of operation 303 may involve different depositionmethods and precursors than in prior cycles of operation 303. Forexample, in one process, tungsten may be deposited into a feature byALD, ALE may be performed to etch the deposited tungsten to open thefeature, and tungsten deposition may be repeated by this time performingCVD of tungsten using a tungsten-containing precursor and a reducingagent to completely fill the feature. In another example, tungsten isdeposited by alternating pulses of WF₆ and BH₄, the tungsten at or nearthe opening of a feature may be etched by alternating pulses of Cl₂ andAr in the presence of a plasma and applying a bias, and tungsten may bedeposited by simultaneous exposure to WCl₅ and H₂.

FIG. 5 provides an example diagram of a timing scheme that may beperformed in accordance with disclosed embodiments. Process 500 includesdeposition cycle 520A, etch cycle 505A, and a repeated deposition cycle520B and etch cycle 505B. Deposition cycle 520A includes W CVD phase503A, which may correspond to operation 303 of FIG. 3. Although a CVDdeposition is provided in FIG. 5, in some embodiments, this operationmay involve cyclic deposition of a metal, such as by ALD. In W CVD phase503A, the carrier gas may be flowed, while the modification chemistryflow is turned off and the removal gas is turned off. CVD Precursors maybe continuously flowed to deposit tungsten and the bias is turned off.Etch cycle 505A may correspond to operations 315 and 335 of FIG. 3. Etchcycle 505A includes a surface modification 515A, which may correspond tooperation 315 of FIG. 3. During surface modification 515A, themodification chemistry is flowed with a carrier gas while the removalgas and CVD precursor flows are turned off. The bias may be on, as shownin FIG. 5. Following surface modification 515A may be a purge phase525A, which, as described above, is an optional operation. During purgephase 525A, the carrier gas is continuously flowed to remove anymodification chemistry that did not adsorb onto the substrate.Accordingly, modification chemistry, removal gas, and CVD precursorflows are turned off, and the bias is also turned off. In removal phase535A, the carrier gas is continuously flowed while the removal gas isflowed, while the modification chemistry and CVD precursor flows areturned off. The bias may also be turned on during removal phase 535A.Removal phase 535A may correspond to operation 335 of FIG. 3. In variousembodiments, a plasma is ignited during this phase. Purge phase 545A mayinvolve flowing a carrier gas while modification chemistry, removal gas,and CVD precursor flows are turned off, and the bias is also turned off.

In accordance with operation 307 of FIG. 3, the operations may berepeated as shown in FIG. 5. Deposition cycle 520B involves W CVD Phase503B, which in this example includes the same flows as in W CVD Phase503A. Here, a carrier gas is flowed with CVD precursors to deposittungsten, while removal gas and modification chemistry flows are turnedoff, and the bias is turned off. In some embodiments, this may furtherpartially fill a feature. Although the same precursors may be used in WCVD Phase 503B as in W CVD Phase 503A, in some embodiments, as describedabove, a repeated operation of 303 of FIG. 3 may involve differentdeposition techniques or precursors. Etch cycle 505B may correspond tooperation 305 of FIG. 3 in a repeated cycle. Etch cycle 505B involves asurface modification 515B, whereby the carrier gas and modificationchemistry are flowed while removal gas and CVD precursor flows areturned off, and a bias is turned on. Purge phase 525B includes carriergas flow while all other flows are turned off, and the bias is turnedoff. Removal phase 535B involves flowing carrier gas with removal gas,while the modification chemistry and CVD precursor flows are turned off.In various embodiments, a plasma is ignited during this phase. The biasis turned on to directionally etch the substrate. Purge phase 545Binvolves flowing carrier gas without flowing modification chemistry,removal gas, or CVD precursors while the bias is turned off.

Embodiments described herein may be integrated with other processes. Forexample, ALE etching can be integrated on a MSSD(Multi-Station-Sequential-Deposition) chamber architecture in which oneof deposition stations can be replaced by an ALE station to allowintegrated deposition/etch/deposition using a similar chemistry forbetter fill and faster throughput capability. Disclosed embodiments maybe performed in some embodiments without breaking vacuum. For example,in some embodiments, disclosed embodiments may be performed in the samechamber or in the same tool. Further examples of apparatuses suitablefor performing disclosed embodiments are described further below.

Apparatus

Inductively coupled plasma (ICP) reactors which, in certain embodiments,may be suitable for atomic layer etching (ALE) operations and atomiclayer deposition (ALD) operations are now described. Such ICP reactorshave also been described in U.S. Patent Application Publication No.2014/0170853, filed Dec. 10, 2013, and titled “IMAGE REVERSAL WITH AHMGAP FILL FOR MULTIPLE PATTERNING,” hereby incorporated by reference inits entirety and for all purposes. Although ICP reactors are describedherein, in some embodiments, it should be understood that capacitivelycoupled plasma reactors may also be used.

FIG. 6 schematically shows a cross-sectional view of an inductivelycoupled plasma integrated etching and deposition apparatus 600appropriate for implementing certain embodiments herein, an example ofwhich is a Kiyo® reactor, produced by Lam Research Corp. of Fremont,Calif. The inductively coupled plasma apparatus 600 includes an overallprocess chamber 624 structurally defined by chamber walls 601 and awindow 611. The chamber walls 601 may be fabricated from stainless steelor aluminum. The window 611 may be fabricated from quartz or otherdielectric material. An optional internal plasma grid 650 divides theoverall process chamber 624 into an upper sub-chamber 602 and a lowersub-chamber 603. In most embodiments, plasma grid 650 may be removed,thereby utilizing a chamber space made of sub-chambers 602 and 603. Achuck 617 is positioned within the lower sub-chamber 603 near the bottominner surface. The chuck 617 is configured to receive and hold asemiconductor substrate or wafer 619 upon which the etching anddeposition processes are performed. The chuck 617 can be anelectrostatic chuck for supporting the wafer 619 when present. In someembodiments, an edge ring (not shown) surrounds chuck 617, and has anupper surface that is approximately planar with a top surface of thewafer 619, when present over chuck 617. The chuck 617 also includeselectrostatic electrodes for chucking and dechucking the wafer 619. Afilter and DC clamp power supply (not shown) may be provided for thispurpose. Other control systems for lifting the wafer 619 off the chuck617 can also be provided. The chuck 617 can be electrically chargedusing an RF power supply 623. The RF power supply 623 is connected tomatching circuitry 621 through a connection 627. The matching circuitry621 is connected to the chuck 617 through a connection 625. In thismanner, the RF power supply 623 is connected to the chuck 617.

Elements for plasma generation include a coil 633 is positioned abovewindow 611. In some embodiments, a coil is not used in disclosedembodiments. The coil 633 is fabricated from an electrically conductivematerial and includes at least one complete turn. The example of a coil633 shown in FIG. 6 includes three turns. The cross-sections of coil 633are shown with symbols, and coils having an “X” extend rotationally intothe page, while coils having a “●” extend rotationally out of the page.Elements for plasma generation also include an RF power supply 641configured to supply RF power to the coil 633. In general, the RF powersupply 641 is connected to matching circuitry 639 through a connection645. The matching circuitry 639 is connected to the coil 633 through aconnection 643. In this manner, the RF power supply 641 is connected tothe coil 633. An optional Faraday shield 649 is positioned between thecoil 633 and the window 611. The Faraday shield 649 is maintained in aspaced apart relationship relative to the coil 633. The Faraday shield649 is disposed immediately above the window 611. The coil 633, theFaraday shield 649, and the window 611 are each configured to besubstantially parallel to one another. The Faraday shield 649 mayprevent metal or other species from depositing on the window 611 of theprocess chamber 624.

Process gases (e.g. metal precursors such as tungsten-containingprecursors, reducing agents, carrier gases, halogen-containing gases,chlorine, argon, etc.) may be flowed into the process chamber throughone or more main gas flow inlets 660 positioned in the upper sub-chamber602 and/or through one or more side gas flow inlets 670. Likewise,though not explicitly shown, similar gas flow inlets may be used tosupply process gases to a capacitively coupled plasma processingchamber. A vacuum pump 640, e.g., a one or two stage mechanical dry pumpand/or turbomolecular pump, may be used to draw process gases out of theprocess chamber 624 and to maintain a pressure within the processchamber 624. For example, the vacuum pump 640 may be used to evacuatethe lower sub-chamber 603 during a purge operation of ALE. Avalve-controlled conduit may be used to fluidically connect the vacuumpump to the process chamber 624 so as to selectively control applicationof the vacuum environment provided by the vacuum pump. This may be doneemploying a closed-loop-controlled flow restriction device, such as athrottle valve (not shown) or a pendulum valve (not shown), duringoperational plasma processing. Likewise, a vacuum pump and valvecontrolled fluidic connection to the capacitively coupled plasmaprocessing chamber may also be employed.

During operation of the apparatus 600, one or more process gases may besupplied through the gas flow inlets 660 and/or 670. In certainembodiments, process gas may be supplied only through the main gas flowinlet 660, or only through the side gas flow inlet 670. In some cases,the gas flow inlets shown in the figure may be replaced by more complexgas flow inlets, one or more showerheads, for example. The Faradayshield 649 and/or optional grid 650 may include internal channels andholes that allow delivery of process gases to the process chamber 624.Either or both of Faraday shield 649 and optional grid 650 may serve asa showerhead for delivery of process gases. In some embodiments, aliquid vaporization and delivery system may be situated upstream of theprocess chamber 624, such that once a liquid reactant or precursor isvaporized, the vaporized reactant or precursor is introduced into theprocess chamber 624 via a gas flow inlet 660 and/or 670.

Radio frequency power is supplied from the RF power supply 641 to thecoil 633 to cause an RF current to flow through the coil 633. The RFcurrent flowing through the coil 633 generates an electromagnetic fieldabout the coil 633. The electromagnetic field generates an inductivecurrent within the upper sub-chamber 602. The physical and chemicalinteractions of various generated ions and radicals with the wafer 619etch features of and deposit layers on the wafer 619.

Volatile etching and/or deposition byproducts may be removed from thelower sub-chamber 603 through port 622. The chuck 617 disclosed hereinmay operate at elevated temperatures ranging between about 10° C. andabout 250° C. The temperature will depend on the process operation andspecific recipe.

Apparatus 600 may be coupled to facilities (not shown) when installed ina clean room or a fabrication facility. Facilities include plumbing thatprovide processing gases, vacuum, temperature control, and environmentalparticle control. These facilities are coupled to apparatus 600, wheninstalled in the target fabrication facility. Additionally, apparatus600 may be coupled to a transfer chamber that allows robotics totransfer semiconductor wafers into and out of apparatus 600 usingtypical automation.

In some embodiments, a system controller 630 (which may include one ormore physical or logical controllers) controls some or all of theoperations of a process chamber 624. The system controller 630 mayinclude one or more memory devices and one or more processors. Forexample, the memory may include instructions to alternate between flowsof modification chemistry such as a chlorine-containing modificationchemistry and a removal gas such as argon, or instructions to ignite aplasma or apply a bias. For example, the memory may include instructionsto set the bias at a power between about 0V and about 200V during someoperations. In some embodiments, the apparatus 600 includes a switchingsystem for controlling flow rates and durations when disclosedembodiments are performed. In some embodiments, the apparatus 600 mayhave a switching time of up to about 500 ms, or up to about 750 ms.Switching time may depend on the flow chemistry, recipe chosen, reactorarchitecture, and other factors.

In some embodiments, disclosed embodiments can be integrated on a MSSD(Multi-Station-Sequential-Deposition) chamber architecture in which oneof deposition stations can be replaced by an ALE station to allow anintegrated deposition/etch/deposition process using a similar chemistryfor better fill and faster throughput capability.

In some implementations, the system controller 630 is part of a system,which may be part of the above-described examples. Such systems caninclude semiconductor processing equipment, including a processing toolor tools, chamber or chambers, a platform or platforms for processing,and/or specific processing components (a wafer pedestal, a gas flowsystem, etc.). These systems may be integrated with electronics forcontrolling their operation before, during, and after processing of asemiconductor wafer or substrate. The electronics may be integrated intothe system controller 630, which may control various components orsubparts of the system or systems. The system controller 630, dependingon the processing parameters and/or the type of system, may beprogrammed to control any of the processes disclosed herein, includingthe delivery of processing gases, temperature settings (e.g., heatingand/or cooling), pressure settings, vacuum settings, power settings,radio frequency (RF) generator settings, RF matching circuit settings,frequency settings, flow rate settings, fluid delivery settings,positional and operation settings, wafer transfers into and out of atool and other transfer tools and/or load locks connected to orinterfaced with a specific system.

Broadly speaking, the system controller 630 may be defined aselectronics having various integrated circuits, logic, memory, and/orsoftware that receive instructions, issue instructions, controloperation, enable cleaning operations, enable endpoint measurements, andthe like. The integrated circuits may include chips in the form offirmware that store program instructions, digital signal processors(DSPs), chips defined as application specific integrated circuits(ASICs), and/or one or more microprocessors, or microcontrollers thatexecute program instructions (e.g., software). Program instructions maybe instructions communicated to the controller in the form of variousindividual settings (or program files), defining operational parametersfor carrying out a particular process on or for a semiconductor wafer orto a system. The operational parameters may, in some embodiments, bepart of a recipe defined by process engineers to accomplish one or moreprocessing steps during the fabrication or removal of one or morelayers, materials, metals, oxides, silicon, silicon dioxide, surfaces,circuits, and/or dies of a wafer.

The system controller 630, in some implementations, may be a part of orcoupled to a computer that is integrated with, coupled to the system,otherwise networked to the system, or a combination thereof. Forexample, the controller may be in the “cloud” or all or a part of a fabhost computer system, which can allow for remote access of the waferprocessing. The computer may enable remote access to the system tomonitor current progress of fabrication operations, examine a history ofpast fabrication operations, examine trends or performance metrics froma plurality of fabrication operations, to change parameters of currentprocessing, to set processing steps to follow a current processing, orto start a new process. In some examples, a remote computer (e.g. aserver) can provide process recipes to a system over a network, whichmay include a local network or the Internet. The remote computer mayinclude a user interface that enables entry or programming of parametersand/or settings, which are then communicated to the system from theremote computer. In some examples, the system controller 630 receivesinstructions in the form of data, which specify parameters for each ofthe processing steps to be performed during one or more operations. Itshould be understood that the parameters may be specific to the type ofprocess to be performed and the type of tool that the controller isconfigured to interface with or control. Thus as described above, thesystem controller 630 may be distributed, such as by including one ormore discrete controllers that are networked together and workingtowards a common purpose, such as the processes and controls describedherein. An example of a distributed controller for such purposes wouldbe one or more integrated circuits on a chamber in communication withone or more integrated circuits located remotely (such as at theplatform level or as part of a remote computer) that combine to controla process on the chamber.

Without limitation, example systems may include a plasma etch chamber ormodule, a deposition chamber or module, a spin-rinse chamber or module,a metal plating chamber or module, a clean chamber or module, a beveledge etch chamber or module, a physical vapor deposition (PVD) chamberor module, a chemical vapor deposition (CVD) chamber or module, an ALDchamber or module, an ALE chamber or module, an ion implantation chamberor module, a track chamber or module, and any other semiconductorprocessing systems that may be associated or used in the fabricationand/or manufacturing of semiconductor wafers.

As noted above, depending on the process step or steps to be performedby the tool, the controller might communicate with one or more of othertool circuits or modules, other tool components, cluster tools, othertool interfaces, adjacent tools, neighboring tools, tools locatedthroughout a factory, a main computer, another controller, or tools usedin material transport that bring containers of wafers to and from toollocations and/or load ports in a semiconductor manufacturing factory.

FIG. 7 depicts a semiconductor process cluster architecture with variousmodules that interface with a vacuum transfer module 738 (VTM). Thearrangement of various modules to “transfer” wafers among multiplestorage facilities and processing modules may be referred to as a“cluster tool architecture” system. Airlock 730, also known as aloadlock or transfer module, interfaces with the VTM 738 which, in turn,interfaces with four processing modules 720 a-720 d, which may beindividual optimized to perform various fabrication processes. By way ofexample, processing modules 720 a-720 d may be implemented to performsubstrate etching, deposition, ion implantation, wafer cleaning,sputtering, and/or other semiconductor processes. In some embodiments,ALD and ALE are performed in the same module. In some embodiments, ALDand ALE are performed in different modules of the same tool. One or moreof the substrate etching processing modules (any of 720 a-720 d) may beimplemented as disclosed herein, i.e., for depositing conformal films,directionally etching films by ALE, etching patterns, and other suitablefunctions in accordance with the disclosed embodiments. Airlock 730 andprocessing modules 720 a-720 d may be referred to as “stations.” Eachstation has a facet 736 that interfaces the station to VTM 738. Insideeach facet, sensors 1-18 are used to detect the passing of wafer 726when moved between respective stations.

Robot 722 transfers wafer 726 between stations. In one embodiment, robot722 has one arm, and in another embodiment, robot 722 has two arms,where each arm has an end effector 724 to pick wafers such as wafer 726for transport. Front-end robot 732, in atmospheric transfer module (ATM)740, is used to transfer wafers 726 from cassette or Front OpeningUnified Pod (FOUP) 734 in Load Port Module (LPM) 742 to airlock 730.Module center 728 inside processing module 720 a-720 d is one locationfor placing wafer 726. Aligner 744 in ATM 740 is used to align wafers.

In an exemplary processing method, a wafer is placed in one of the FOUPs734 in the LPM 742. Front-end robot 732 transfers the wafer from theFOUP 734 to an aligner 744, which allows the wafer 726 to be properlycentered before it is etched or processed. After being aligned, thewafer 726 is moved by the front-end robot 732 into an airlock 730.Because the airlock 730 has the ability to match the environment betweenan ATM 740 and a VTM 738, the wafer 726 is able to move between the twopressure environments without being damaged. From the airlock 730, thewafer 726 is moved by robot 722 through VTM 738 and into one of theprocessing modules 720 a-720 d. In order to achieve this wafer movement,the robot 722 uses end effectors 724 on each of its arms. Once the wafer726 has been processed, it is moved by robot 722 from the processingmodules 720 a-720 d to the airlock 730. From here, the wafer 726 may bemoved by the front-end robot 732 to one of the FOUPs 734 or to thealigner 744.

It should be noted that the computer controlling the wafer movement canbe local to the cluster architecture, or can be located external to thecluster architecture in the manufacturing floor, or in a remote locationand connected to the cluster architecture via a network. A controller asdescribed above with respect to FIG. 6 may be implemented with the toolin FIG. 7.

EXPERIMENTAL Experiment 1

Etch rate of tungsten was plotted against chlorination bias power foretch with chlorine adsorption and no argon sputtering, as well as for anatomic layer etch (ALE) process with chlorine adsorption with argonsputtering. The results are plotted in FIG. 8. The dotted line depictsthe etch rate of tungsten versus chlorination bias (e.g., the bias powerduring chlorine adsorption) for a process involving adsorbing chlorineand igniting a plasma at 900 W, and no argon sputtering. The solid linedepicts the etch rate of tungsten versus chlorination bias for a processinvolving adsorbing chlorine and igniting a plasma at 900 W, followed byan argon bombardment with a bias power of 60V. A chlorination biasthreshold voltage as shown in FIG. 8 is at about 60V. Note where achlorination bias is less than 60V, tungsten is not etched without usingion bombardment of argon. Where a chlorination bias is greater than 60V,the etch rate of tungsten without argon ion bombardment is much lowerthan that of the process with argon ion bombardment. These resultssuggest that argon ion bombardment may be used to modulate the etch rateof tungsten by ALE methods in various embodiments whereby 1) chlorine isbeing adsorbed onto the tungsten substrate without etching duringchlorination, and 2) the bias power during ion bombardment of argon iscontrolled to reduce or prevent physical removal (or sputtering) bysetting the bias power lower than the sputter threshold.

Experiment 2

An experiment was conducted on a substrate with a feature to be filledwith tungsten. The feature was lined with a titanium nitride (TiN)barrier layer. Tungsten was nucleated on the surface of the feature andtungsten was deposited by atomic layer deposition (alternating pulses ofWF₆ and B₂H₆). FIG. 9A shows a 20 nm feature 912 in a substrate 910lined with TiN barrier layer 914 and a conformally tungsten layer 916.An opening 918 a is shown at the top of the feature.

The substrate in FIG. 9A is exposed to 10 cycles of ALE involvingalternating pulses of (1) Cl₂/BCl₃ with an in situ inductively coupledplasma power of 900 W and no bias at 60° C., and (2) argon gas at alower pressure than (1) with a 300 W plasma and a 60 Vb bias at 60° C.The resulting substrate is shown in FIG. 9B. Note the opening 918 b isopened to thereby allow subsequent deposition of tungsten into thefeature to completely fill the feature. Table 1 below shows themeasurements for the thickness of tungsten deposited in various parts ofthe substrate, as well as the trench opening and average thickness ofthe TiN barrier. Measurements are shown in nanometers.

TABLE 1 Pre and Post ALE Measurements Pre-ALE 10 cycles of ALEMeasurements (nm) nm nm nm/cycle W film Top surface 6.9 3.3 0.36thickness Top corner 6.1 3.0 0.31 Trench sidewall, ⅙ 5.9 4.4 0.15 trenchdepth Trench sidewall, ⅓ 5.8 5.0 0.08 trench depth Trench sidewall, ⅞5.9 5.9 0.00 trench depth Trench bottom 5.7 5.3 0.04 Average TiN barrier3.0 3.0

The substrate was further exposed to 5 more cycles of ALE involvingalternating pulses of (1) Cl₂/BCl₃ with an in situ inductively coupledplasma power of 900 W and no bias at 60° C., and (2) argon gas at alower pressure than (1) with a 300 W plasma and a 60 Vb bias at 60° C.The resulting measurements are shown in Table 2 below.

TABLE 2 Pre and Post ALE Measurements Pre-ALE 15 cycles of ALEMeasurements (nm) nm nm nm/cycle W film Top surface 6.9 2.0 0.49thickness Top corner 6.1 1.4 0.47 Trench sidewall, ⅙ 5.9 4.1 0.18 trenchdepth Trench sidewall, ⅓ 5.8 3.9 0.19 trench depth Trench sidewall, ⅞5.9 5.6 0.03 trench depth Trench bottom 5.7 5.0 0.07 Average TiN barrier3.0 3.0

These results suggest that disclosed embodiments allow for precisecontrol of the amount of tungsten film etched depending on the number ofcycles, the parameters, and other factors. For example, to etch moretungsten, more cycles may be performed. The results in Table 2 suggestsome tungsten recess due to the ALE process but subsequent cycles ofdeposition of tungsten can recover the tungsten etched in ALE. The TiNbarrier remains on the substrate, and etch cycles of ALE may bemodulated to ensure that there remains sufficient tungsten on thesurface of the feature so as not to expose the TiN barrier layer.

CONCLUSION

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, it will be apparent thatcertain changes and modifications may be practiced within the scope ofthe appended claims. It should be noted that there are many alternativeways of implementing the processes, systems, and apparatus of thepresent embodiments. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the embodiments arenot to be limited to the details given herein.

What is claimed is:
 1. A method comprising: preferentially etching afirst amount of a metal in a feature on a substrate at or near anopening of the feature relative to an interior region of the feature by(i) exposing the feature to a halogen-containing gas to form a modifiedsurface of the first amount of the metal; (ii) exposing the modifiedsurface to an activation gas; and (iii) applying a bias to the substrateduring at least one of (i) and (ii) using a bias power.
 2. The method ofclaim 1, wherein the metal contains tungsten or molybdenum.
 3. Themethod of claim 1, wherein the bias power when applied during (i) isgreater than OV and less than about 200 V.
 4. The method of claim 1,wherein the bias power when applied during (ii) is less than a thresholdbias power.
 5. The method of claim 1, wherein the forming of themodified surface of the first amount of the metal is self-limiting. 6.The method of claim 1, further comprising depositing the first amount ofthe metal in the feature on the substrate, wherein the depositing andthe preferentially etching are performed without breaking vacuum.
 7. Themethod of claim 6, wherein the depositing and the preferentially etchingare performed in different chambers of the same tool.
 8. The method ofclaim 1, further comprising igniting a plasma during at least one of (i)and (ii).
 9. The method of claim 1, further comprising, afterpreferentially etching the first amount of the metal, depositing asecond amount of metal in the feature.
 10. The method of claim 9,wherein the metal is tungsten deposited using one or more tungstenprecursors or combinations thereof.
 11. The method of claim 9, whereinthe metal is selected from the group consisting of fluorine-freetungsten, titanium, tantalum, nickel, and cobalt.
 12. The method ofclaim 1, wherein the halogen-containing gas is selected from the groupconsisting of chlorine, bromine, iodine, and combinations thereof. 13.The method of claim 1, wherein the activation gas is selected from agroup consisting of helium, neon, krypton, and argon.
 14. A methodcomprising: preferentially etching a first amount of a metal in afeature on a substrate at or near an opening of the feature relative toan interior region of the feature by (i) exposing the feature to ahalogen-containing gas to form a modified surface of the first amount ofthe metal; and (ii) exposing the modified surface to an activation gasat a chamber pressure between about 1 mTorr and about 15 mTorr.
 15. Themethod of claim 14, wherein the metal contains tungsten or molybdenum.16. The method of claim 14, wherein forming of the modified surface ofthe first amount of the metal comprises a self-limiting reaction. 17.The method of claim 14, further comprising depositing the first amountof the metal in the feature on the substrate, wherein the depositing andthe preferentially etching are performed without breaking vacuum. 18.The method of claim 14, further comprising igniting a plasma during atleast one of (i) and (ii).
 19. The method of claim 14, furthercomprising, after preferentially etching the first amount of the metal,depositing a second amount of metal in the feature.